In recent years, the multifunctionalization of mobile communication terminals has been progressing rapidly. Consequently, a mobile communication terminal is provided with an integration of functions implemented by electronic apparatuses such as a personal computer, a digital video and digital camera. With this multifunctionalization, the types of user data that the user stores in his/her mobile communication terminal have become widely varied. In addition, the maximum amount of each user data tends to grow. Besides, there are increasing opportunities to handle highly confidential data, as for example in the case where electronic money or cash function is used, with the mobile communication terminal.
As such, since the mobile communication terminal comes to store various types of/large amounts of user data, if the data are lost due to the damage, loss, etc. of the terminal, the trouble for the user is even more serious. In order to solve the problem, there have been proposed systems for backing up user data stored in the mobile communication terminal. For example, Japanese Patent Application laid open No. 2004-112478 discloses a data backup system for automatically and regularly backing up user data stored in a mobile communication terminal to a server or the like via a communication network. The data backup system automatically backs up user data, and eliminates the user's need to back up the data via a dedicated cable, etc., thus improving convenience for the user. Moreover, because regular backups of user data are performed, almost the latest information can always be backed up, which further improves convenience for the user.
The conventional backup system, however, transmits all user data to back up. In other words, data that do not need backup are also transmitted each and every time. Therefore, network traffic and transmission time required of the backup substantially increase. As a result, the mobile communication terminal cannot be used for another purpose during the transmission of backup data, and convenience to the user is reduced. Additionally, the inefficient use of radio bands causes lack of lines in the entire system. Further, various usage modes of the mobile communication terminal are not properly supported, and, for example, highly confidential data is at risk of eavesdropping.